WESM zl Management and Configuration Guide WT.01.28 and greater

9-7
Fast Layer 2 Roaming and Layer 3 Mobility
Overview
■ The modules store information about all stations associated to any module in the
Layer 3 mobility domain.
The Wireless Edge Services zl Module responsible for handling a station’s traffic
is that station’s home module (HM). All the peers in the Layer3 roaming domain
must track all stations’ HM and HM VLAN. A module can then recognize when
a station that roams to it requires a Layer 3 roam: the station’s HM VLAN is
different from the VLAN supported on that module.
■ When a Layer 3 roam is necessary, a module tunnels traffic back to the station’s
original module.
Each peer in the Layer 3 mobility domain maintains a Generic Routing Encap-
sulation (GRE)-like tunnel to each other peer. (The peers automatically configure
the tunnel when you enable Layer 3 mobility.) When a station roams, the module
tunnels all traffic to and from the station, including Dynamic Host Configuration
Protocol (DHCP) and Address Resolution Protocol (ARP) requests, to the
station’s HM.
As you plan Layer 3 roaming, keep in mind that a Layer 3 roaming domain should
be contiguous with the following two domains. (See Figure 9-2.)
■ The Radio Frequency (RF), or Layer 2, roaming domain
Layer 3 roaming takes place in the background on top of RF roaming. That is,
at both Layer 2 and Layer 3, stations always roam within a WLAN. (Moving to
a new WLAN requires the user to select a new wireless network.) Therefore, all
Wireless Edge Services zl Modules in the Layer3 roaming domain must support
the WLAN in question.
In addition, you must not divide a WLAN into multiple Layer 3 roaming
domains.
■ A ProCurve Identity Driven Manager (IDM) location domain
If you use IDM to assign network rights, best practices dictate that devices in
the same Layer 3 roaming domain are also in the same location domain.
Note, however, that you cannot use dynamic VLAN assignments with Layer 3
mobility.
For seamless Layer 2 roaming for WLANs that use Web-Auth, you must place all
Wireless Edge Services zl Modules in the same redundancy group. So, if you want
to enable Layer 3 mobility as well, you should place modules in the same redundancy
group and Layer 3 mobility domain.